Method of manufacturing a nuclear fuel assembly spacer

ABSTRACT

A method for manufacturing an expanded sheet spacer for nuclear fuel rod assemblies is presented. In general the method has the first step of forming a plurality of spaced slits along parallel lines on a sheet material so that each slit has a length of at least two times the distance between pairs of slits and the center of each slit is located adjacent the space between slits of the next line of slits. The second step of the method is bending the sheet below each slit perpendicular to the slits so that a portion of the sheet below each slit is displaced in the same direction away from the original plane of said sheet and a plurality of channels having axes substantially parallel to each other and to the plane of the sheet are formed.

United States Patent [1 1 Ripley 1451 Feb. 5, 1974 1 1 METHOD OFMANUFACTURING A NUCLEAR FUEL ASSEMBLY SPACER [75] Inventor: Charles C.Ripley, San Jose, Calif.

[73] Assignee: General Electric Company, San

Jose, Calif.

1221 Filed: Mar. 15, 1971 211 Appl. No.: 124,319

Related U.S. Application Data [62] Division of Ser. No. 772,206, Oct.31, 1968.

[56] References Cited 1 UNITED STATES PATENTS 184.517 3/1905 Curtis29/6.l 1.086.027 Z/l9l4 Clark 29/6.1 X

1.165071 12/1915 Clark 29/6.2 2.018.085 10/1935 Otte 29/6.2 X

3.070.198 12/1962 Haskell 29/6.l X

3.281.327 10/1966 Webb et al. 176/78 X 1,379,617 4/1968 Andrews et al176/78 3,459,026 8/1969 Allen et al. 29/l63.5 R X FOREIGN PATENTS ORAPPLICATIONS 895,739 5/1962 Great Britain 176/78 Primary ExaminerCharlesW. Lanham Assistant ExaminerVictor A. DiPalrna Attorney, Agent, orFirm-Ivor J. James, Jr.; Sam E. Laub; Samuel E. Turner [5 7] ABSTRACT Amethod for manufacturing an expanded sheet spacer for nuclear fuel rodassemblies is presented. In general the method has the first step offorming a plurality of spaced slits along parallel lines on a sheetmaterial so that each slit has a length of at least two times' thedistance between pairs of slits and the center of each slit is locatedadjacent the space between slits of the next line of slits. The secondstep of the method is bending the sheet below each slit perpendicular tothe slits so that a portion of the sheet below each slit is displaced inthe same direction away from the original plane of said sheet and aplurality of channels having axes substantially parallel to each otherand to the plane of the sheet are formed.

5 Claims, 15 Drawing Figures gees Patented Feb. 5, 1974 3,789,476

8 Sheets-Sheet l INVENTOR:

Fig 2 CHARLES c. RIPLEY Patented Feb. 5, 1974 8 Sheets-Sheet 2 Fig. 3

Fig. 4a

Patented Feb. 5, 1974 3,789,476

8 Sheets-Sheet 3 Patented Feb. 5, 1974 8 Sheets-Sheet 4 Patented Feb. 5,1974 8 Sheets-Sheet Patented Feb. 5, 1974 3,789,476

8 Sheets-Sheet 6 as Fig. 9

Fig. IO

Patented Feb. 5, 1974 8 Sheets-Sheet '7 Fig. I2

Patented Feb. 5, 1974 3,789,476

8 Sheets-Sheet 8 METHOD OF MANUFACTURING A NUCLEAR FUEL ASSEMBLY SPACERThis application is a divisional of US. Pat. application Ser. No.772,206, entitled Nuclear Fuel Assembly Spacer", filed Oct. 3l, 1968 byCharles C. Ripley.

BACKGROUND OF THE INVENTION Nuclear chain fission reactions and thereactors in which they take place are now well known. A typical reactorincludes a chain reacting assembly or core made up of nuclear fuelmaterial contained in fuel elements. The fuel material is generallyincased in a corrosion resistant heat conductive shell or cladding. Thereactor core, made up of a plurality of these elements in spacedrelationship, is enclosed in a container through which the reactorcoolant flows. As the coolant passes between the spaced fuel elements,it is heated by thermal energy released in the fuel material during thefission reaction. The heated coolant then leaves the reactor. thethermal energy is used to perform useful work and the now-cooled coolantis recycled back to the reactor.

in modern water cooled commercial reactors, such as those described inUS. Pat. No. 3,029,197, the core is generally made up of a plurality ofsub-assemblies or bundles, each of which consists of a plurality ofrodshaped fuel elements held in a spaced parallel relationship.Typically a bundle may contain 49 fuel rods having a diameter of about0.5 inch and a length of about 12 feet. The rods are maintained in thedesired arrange ment by tie plates at each end and several lateralspacing and support means along the bundle length. In fast breeder typereactors, each bundle may contain as many as 750 rods, each having adiameter of 0.25 inch or less. Maintaining this number of very thin rodsin the desired parallel array is especially difficult.

Spaced fuel rods located within a bundle may experience different ratesof heat generation and resulting locally different temperatures. Thiscondition may be the result of flux peaking in adjacent coolantchannels, unequal distribution of coolant flow through the core,presence of adjacent structural material and the like. Accordingly, thespaced fuel rods are subject to unequal thermal expansions so thatunless restraining means are provided the rods and bundles are subjectto deformation or bowing. This may cause local hot spots where adjacentrods touch resulting in the decomposition or melting of the cladmaterial. This may lead to the formation of cracks or openings in theclad which directly expose the fuel and fission product gases containedwithin the fuel rod to the coolant. When this occurs, not only must thefuel elements be replaced, requiring shutdown of the reactor, but thecoolant will be contaminated with radioactive material. Also, severebowing of peripherally located fuel rods may interfere with control rodmovement.

Therefore, the intermediate spacers must have sufficient strength toprevent rod bowing due to temperature variations. ln addition, thespacer must have sufficient strength to resist severe thermal andhydraulic forces which vary greatly beteen reactor starting conditionsand hot full power operating conditions.

n the other hand, excessively large and sturdy spacers may detrimentallyaffect reactor performance. If the spacer locally restricts coolantflow, local hot spots may occur causing local cladding failure asdescribed above. The spacer should be as small as possible and have alow absorption cross-section for neutrons so as to minimize parasiticabsorption. This absorption becomes significant where a great manyspacers are required in the core. Desirably, the spacers are fabricatedfrom a material, such as zirconium alloy, which has low neutronabsorption and sufficient strength.

Spacers which are complex and difficult to fabricate are undesirable,since a great many spacers are required in a single core and preferredmaterials, such as zirconium are difficult to fabricate in complexshapes. Similarly, spacer designs requiring a great many welds aredifficult to consistently fabricate within the necessary tolerances.

If the contact area between the spacer and each fuel rod is too great,coolant flow to that area may be restricted, resulting in a hot spot.Conversely, if the contact area is too small, differential thermalexpansion and vibrations induced by coolant flow may cause frettingdamage to the clad at the contact point. Eventually, the damaged surfacemay crack, allowing the coolant to contact the fuel within the rod. Inaddition, loading fuel rods into a tight-fitting spacer may scratch orotherwise damage the surface of the rods.

Thus there is a continuing need for improvd fuel rod assembly spacingand support means.

SUMMARY OF THE INVENTION It is, therefore, an object of this inventionto provide a nuclear fuel assembly spacer overcoming the abovenotedproblems.

Another object of this invention is to provide a nuclear fuel assemblyspacer which is simple and inexpensive to fabricate.

Another object of this invention is to provide a nuclear fuel assemblyspacer having an optimum balance of high strength and low parasiticabsorption.

Still another object of this invention is to provide a nuclear fuelassembly spacer into which fuel rods may be easily loaded withoutsurface damage to the rods.

Yet another object of this invention is to provide a nuclear fuelassembly spacer of improved coolant flow guiding characteristics.

The above objects, and others, are accomplished in accordance with thisinvention by providing a nuclear fuel assembly spacer comprising anexpanded sheet structure containing a plurality of short slits spacedalong spaced parallel lines. Preferably, a small round stress relievinghole is formed at the end of each slit. The length of each slit is atleast about 2 times the length of the space along the line between theends of adjacent slits. Portions of the sheet below the center of eachslit are all displaced in the same direction away from the originalplane of the sheet. A plurality of channels having axes substantiallyparallel to each other and to the original plane of the sheet result.Each channel has an approximately hexagonal or square cross section.Preferably, at least several of the walls of each channel are dimpledinwardly, to support a rod projecting through the channel out of generalcontact with the walls of the channel.

In a preferred embodiment, the length of each slit is about three timesthe distance between the ends of adjacent slits, and the center of theslits in one row are adjacent the center of the inter-slit space in thenext row. This configuration results in the formation of channels eachhaving a hexagonal cross-section. This is especially advantageous, sincethree inwardly projecting dimples may be provided, in every-other wallof each hexagonal channel to support the fuel rod. The three walls ofthe channel which do not have an inwardly projecting dimple have anoutwardly projecting dimple projecting into the next channel. Thus,back-to-back dimples in a single wall are never required. Back-tobackdimples are disadvantageous, since they will resist flexing as fuel rodsthermally expand in diameter because they form a substantially rigidconnection between adjacent fuel rods. The arrangement of single dimplesprovided in the hexagonal channels according to this invention willpermit flexing of the channel walls to accommodate thermal expansion.

The one-piece multi-channel spacer thus produced may then be subdivided,or the outer edges may be trimmed, to produce a spacer which will hold aplurality of fuel rods in the desired manner. For example, the spacermay be trimmed to a hexagonal or rectangular overall shape.

In an especially preferred embodiment, the spacer may be trimmed to ashape corresponding to /s of a hexagon. Three such spacers may be joinedtogether to form a hexagonal bundle having desirable flowcharacteristics, as is further discussed below.

DETAILED DESCRIPTION OF THE INVENTION Details of the invention and ofthe preferred embodiments thereof will be further understood uponreference to the drawings wherein:

FIG. 1 is a plan view of a spacer according to this invention;

FIG. 2 is an isometric view of the spacer shown in FIG. I, seen from theviewpoint indicated by line 22 in FIG. 1;

FIG. 3 is an isometric view of one section of the spacer shown in FIG.I, seen from the viewpoint indicated by line 33 in FIG. 1;

FIG. 4a is an isometric view of one section of the spacer shown in FIG.1 showing a modification thereof;

FIG. 4b is an isometric view of a portion of the spacer shown in FIG. 1,showing a second modification thereof;

FIG. 5 is a plan view of preform from which the spacer shown in FIG. 1is formed;

FIG. 6 is a front elevation view of a machine for forming the spacers ofthis invention;

FIG. 7 is a side elevation view of the machine shown in FIG. 6;

FIGS. 8, 9 and 10 show a typical cams for use in the machine shown inFIGS. 6 and 7;

FIG. 11 is an isometric view of a portion of the machine shown in FIGS.6 and 7 detailing the sheet forming means;

FIG. 12 is an elevation view of a portion of the ram and support sheetforming means;

FIG. 13 is an isometric view of an alternative embodiment of the spacershown in FIG. 1; and

FIG. 14 is an isometric view of a second alternative embodiment of thespacer.

Referring now to FIG. 1 there is seen a spacer according to thisinvention which is suitable for supporting a plurality of nuclear fuelrods in hexagonal array. The spacer, generally designated 10, is adaptedto be positioned within an elongated hexagonal shroud, gen erallyindicated by broken lines 11. Spacer 10 is made up of three identicalsegments or sections l2, l3 and 14. The dividing lines between sectionsare symbolically indicated by heavy black lines l5, l6 and 17 in FIG. 1with each of the numbers also representing one of a plurality ofparallely spaced regularly deformed wall portions with each wall portionbeing displaced in a tiered manner from the adjacent wall portion.Adjacent spacer sections are joined together, such as by welding, alongthese lines l5, l6 and 17. Each of sections l2, l3 and I4 is formed, asdescribed in detail below, from a single sheet of metal. The formingoperation produces a plurality of generally hexagonal parallel openings18. The center fuel rod opening 19 is formed by the outer walls of eachsection where they come together at the center of the assembly.

As best seen in FIGS. 1 and 2, small centering dimples 20 are providedin the wall portions (e.g., 12, 13 and 14) of each fuel rod opening.Each opening has three spaced dimples to assure correct positioning. Asseen in FIG. 2, the longer fuel openings may have dimples at each end,if desired.

FIG. 2 shows an isometric view of the fuel assembly taken from thedirection indicated by line 22 in FIG. 1. Thus, FIG. 2 shows two fullspacer sections, namely sections 12 and 13. When positioned in a reactorcore with the spacer apex upward, flow through the spacer will beslightly redirected away from the shroud walls towards the center of theassembly since there is a generally pyramidal cavity extending up intothe bottom of the spacer conforming in shape to the spacer apex as seenin FIG. 2. It is generally desirable to increase flow through the centerof the fuel bundle since the center fuel rods generally have the highestheat output.

As seen in FIGS. 2 and 3, the spacer sections may be convenientlysecured together by means of a row of tabs 23 along one edge of eachspacer section which meet with a corresponding row of cutouts 24 in theadjacent wall. Thus, when the spacer sections are assembled as seen inFIG. 1, the tabs 23 of one section will fit into cutouts 24 in the nextadjacent section. The tabs may be secured in place such as by welding.Thus, the wall thickness beteween adjacent spacer sections is notincreased.

FIG. 3 shows an isometric view of the spacer taken in the directionshown by line 33 in FIG. 1. Thus, FIG. 3 shows a view of a single spacersection 13.

FIGS. 4a and 4b show details of modifications to portions of the spacersection shown in FIG. 3. FIG. 4a shows an alternate skirt form in whicha reinforcing band 26 is formed along and as part of the lower edge ofthe spacer section. The reinforcement is produced by die forming thisedge after the channels have been formed. The space between band 26 andthe wall of the sector is thus filled with outwardly projecting fillets27 formed from the spacer material. This alternate arrangement serves toreinforce the spacer and to additionally direct coolant flow away fromthe shroud wall and towards the center of the fuel bundle.

FIG. 4b shows a second alternate arrangement corresponding to the viewseen in FIG. 3, in which the lower edge of the spacer section is cutaway and is stepped up in a manner corresponding to the upper surface ofeach fuel rod opening. This alternative decreases the amount ofparasitic neutron absorbing material included in the spacer. Of course,if desired, a reinforcing band such as is shown in FIG. 4a could beincorporated into the embodiment shown in FIG. 4b. This configurationaids in directing coolant flow from along the shroud wall towards thecenter of the fuel assembly. The size of each opening 18 is about threetimes the distance between adjacent openings on the visual line ofopenings formed between each pair of adjacent wall portions as shown inFIGS. 2, 3 and 4.

Each of the spacer sections shown in FIGS. 1-4 is formed from a singleflat metal sheet. FIG. 5 shows such a sheet from which a spacer sectionsuch as is shown in FIG. 4b may be formed.

The preform shown in FIG. 5, when deformed as described below, willresult in a spacer corresponding to one section of the combinationspacer shown in FIG. 1 with the lower edge modified as shown in FIG. 4b.The preform is cut from a sheet of suitable metal, such as a zirconiumalloy or a stainless steel, typically having a thickness of about mils.The preform and the various openings therein may be cut by any suitableshearing, diecutting or chemical etching type operation.

The outline of the preform will vary depending upon the desired shape ofthe spacer to be produced, e.g., hexagonal. triangular or rectangular.All hexagonal channel spacers will have the same pattern of slits 30formed over the surface thereof. These slits 30 are arranged on parallellines with each slit having a length substantially equal to three timesthe space between adjacent slits along a given line. Where a pattern ofsquare-shaped channel openings is to be formed (as shown in FIG. 13,below) slits 30 will have a length equal to twice the space betweenadjacent slits. In each case each slit will be aligned with theinter-slit space on the lines above and below the given line.

Desirably, slits 30 have rounded ends 31 to minimize stressaccumulations. Where the slits are relatively wide, as shown in FIG. 5,the ends need merely be rounded as shown. Where the slits are formed bymerely cutting along the line and not removing material, it is desirablethat small round holes be formed at the ends of the slits.

As seen in FIG. 5, the lower edge of the preform steps upwardly,alternating between diagonal and horizontal steps, so that the resultingspacer will have the configuration shown in FIG. 4b. To produce thelower edge configuration shown in FIGS. 1 3, the lower edge of thepreform would be a straight line extension of lower edge 33, formingright angles with lines extended downwardly from end lines 34 and 35.

The upper edge of the preform is stepped upwardly and inwardly so thatthe spacer will have the configuration shown in FIGS. 1-3. While thespacer sections may be secured together in any desirable manner, thetabs 37 and openings 38 provide an especially preferred multi-partspacer assembly system. As seen in FIG. 1, the tabs 37 on one spacersection fit into openings 38 on the next adjacent spacer section. Thetabs may be secured to the opening edges by any suitable method, such aswelding. Thus, only a single sheet of material is present betweenadjacent spacer sections because of the interlocking nature of theassemblies.

Preferably, dimples 40 are provided in the walls of each individual fuelrod holding channel to hold the fuel rod out of general contact with thechannel wall. As seen in FIG. I, the dimples may be formed so that everyother wall of a given hexagonal channel has an inwardly projectingdimple. Thus, each fuel rod is supported by three equally spaceddimples. Since there are never two dimples in the same planar wall,back-toback, the channels may flex slightly as the fuel rods expand. Thenext adjacent fuel rod channel suffers no adverse dimple pressureagainst its own rod. Also, the dimples are located in differenthorizontal planes (that is, planes perpendicular to the centerline ofthe fuel bundles) so that a slight twisting of the channel walls maytake place during fuel expansion.

As is apparent, this preform may be easily and simply fabricated usingmodern diecutting techniques. The configuration of the outer edges ofthe preform maybe widely varied depending upon the ultimate outer shapeof the desired spacer. The dimples may be formed by a single diepressing operation between mating dies, with certain dimples projectingupwardly and others downwardly from the plane of the preform. Thepreform is then reshaped into the spacer configuration by simple diepressing techniques.

FIGS. 6 and 7 show front and side elvation views of a typical diepressing machine useful in forming a preform such as shown in FIG. 5into a spacer section such as that shown in FIG. 3.

Preferably, the preform is first roughly shaped by stretching thepreform between gripping points along the upper and lower edges in themanner in which expanded metal mesh is formed. This stretching operationwill open the slits into rounded openings approximating the hexagonalopenings ultimately to be produced.

As seen in FIGS. 6 and 7, the spacer is formed between a lower dieassembly made up of a plurality of aligned plates, which conforms to theshape of the desired spacer. Plates 51 are held in alignment by a bolt53 which passes through plates 51 and a backing plate 54. A pair ofupwardly projecting V-shaped notches 55 rest on a pair of cylindricalsupport members 56. This engagement between notches 55 and cylinders 56assures proper alignment between die assembly 50 and the remainder ofthe machine whenever die assembly 50 is removed and replaced.

A plurality of cooperating punches 58 are located above die assembly 50to sequentially press the preform against portions of the die assemblyto form the spacer. Details of the punches and die assembly are shown inFIGS. 11 and 12, below. Each of the punches 58 is biased upwardly bysprings 59 mounted on rods which extend from bar 60 upwardly through theindividual punches 58 to support member 61. Thus, the entire array ofpunches 58 depends from support member 61 in a manner which permits oneor more of the punches 58 to be pushed downwardly against die assembly50.

Support bar 61 is mounted on a frame including tubular members 63surrounding vertical supports 64 which are secured to a base 65 on whichdie assembly 50 is mounted. The upper end of tubular members 63 aresecured to a cross member 67 which is connected to an hydraulic cylinder68. Thus, hydraulic cylinder 68 is adapted to raise and lower the entireassembly including the array of punches 58. After the preform is placedover die assembly 51, hydraulic cylinder 68 is actuated to lower theassembly until the upper center portion 70 of die assembly 51 engagesthe center punch 71 of punch array 58. This serves to hold the preformfirmly in position.

The remaining punches 58 are then sequentiallybrought downwardly againstthe preform to press it into contact with die assembly 51 to form thespacer. This sequential operation is caused by a plurality of cams 74fixed to and rotatable with a shaft 75 rotated by a spur gear 76 drivenby an hydraulic cylinder 77 through a rack 78. Pillow blocks 80 mountedon support member 61 support shaft 75 for rotation.

As shown in detail in FIGS. 8-10, the cams 74 are shaped so that theysequentially press down punches 58 from the center outwardly. Thus, atthe completion of the spacer forming sequence, all of the punches 58 arein engagement pressing the preform against the die assembly 51. Thepreform is released by raising rack 78 and/or raising the assembly madeup of support member 61, tubular member 63 and cross bar 64 by means ofhydraulic cylinder 68. The shaped spacer section is then removed and theabove-described sequence repeated with another preform.

FIGS. 8, 9 and show side views of three typical cams useful as part ofcam array 74 for actuating punches 58. Each of the cams has an opening82 through which shaft 75 passes. Key ways 83 are provided for a keywhich locks the cam to shaft 75. The cams shown in FIGS. 8, 9 and 10 aretypical of the many cams which would be used in this machine. The camsshown on FIG. 8 have a generally cylindrical surface 84 over all but asmall portion of the circumference. Cams having this configuration wouldbe located on both sides of the center, near the center of the camarray. As this cam rotated the punch would be pressed down when point 86engaged the punch. The punch would be held in engagement with dieassembly 51 throughout approximately 270 of the rotation of shaft 75.The next pair of cams outwardly adjacent the cams shown in FIG. 8 wouldhave a configuration such as shown in FIG. 9. Here a larger portion ofthe cam surface projects inwardly from the generally cylindrical surface87. As this cam rotated together with that shown in FIG. 8, first thepunches engaged by cams of FIG. 8 would be depressed then those engagedby the cams shown in FIG. 9 would shortly thereafter be depressed.Additional cams having cylindrical surfaces of lesser extent wouldsequentially press down the other punches beginning at the center of thearray and working outwardly. A typical cam which might drive theoutermost punches is shown in FIG. 10. As seen in this figure, thecylindrical surface extends only over a small portion of the camsurface. Thus, as can be seen in FIG. 10, this cam would rotateapproximately 270 before the corresponding punches were depressed aspoint 88 reached the punch surface. These cams are merely typical of themany designs which could be used in cooperation with a punch array. Itis merely necessary that the cams actuate the punches in order tosequentially form portions of the spacer.

Details of the cooperative relationship between punch assembly 58 anddie assembly 50 will be seen in FIG. 11 which shows an isometric view ofa portion of the machine shown in FIGS. 6 and 7. As seen in FIG. 11,each of the raised portions 90 have a depression 91 formed in the uppersurface thereof to receive the dimples 40 in the preform and preventdistortion thereof. Each of the plates 51 which make up die assembly 50can be produced by conventional machining techniques. Each of thepunches 93 which engage a raised portion 90 have a flat surface whichengages the upper portion of raised portion 90 and two lips 94 to formthe channel corners. Punches 93 are cut away slightly at the corner 95to prevent direct pressure on the preform at the corner of raisedportion 90. The punches 97 which engage those portions of die 50adjacent raised portions have a flat face directly engaging faces 98 ondie members 50. Thus, as the cams actuate the punches, first punch 93 isbrought into engagement with lips 94 bending the preform around thecorners of raised portion 90 and holding the preform thereagainst. Thenpunches 97 are brought into engagement pressing the preform down againstflat faces 98. Broken lines 96 symbolically show the forward travel ofpunches 97 relative to punch 93, after punch 93 has engaged raisedportion 90. This operation continues in sequence with additional similarpunches until the entire spacer is formed.

Details of the engagement of the spacer preform with the punch and diearray is further detailed in FIG. 12, which shows an elevation view of aportion of the punch and die assembly. As seen in FIG. 12, preform 29has been shaped to conform to the upper surface of die assembly 50.Downwardly extending dimples 40 extend into depressions 91 and raisedportions 90 of the die assembly. Upwardly projecting dimples 40 rest onthe angled walls of upward projections 90 between punches 93 and 95.Thus, the spacer is sequentially formed by the sequentially operatedpunches without deforming the dimples 40.

While the above described machine and method for forming the spaces ofthis invention is efficient and reliable, any other suitable system maybe used if desired. Of course, the form of the punches and dies may bevaried widely depending upon the spacer configuration desired.

An alternative embodiment of the spacer of this invention, especiallysuitable for use where the fuel assembly is in a square array, is shownin FIG. 13. Here, the assembled spacer is made up of four symmetricalspacer sections 99. The fuel rod receiving openings are square in crosssection rather than hexagonal. Preferably, dimples (not shown) will beformed in each wall portion of each fuel rod receiving channel so thatfour dimples project into each channel, one from each of the four wallportions. An arrangement of corresponding tabs 100 and openings 10],such as are described above, are provided for securing the spacersections together. These spaces may be formed in a machine such as thatshown in FIGS. 6 and 7, with the punches and dies modified to form thesquare rather than hexagonal channel openings 102. The size of eachopening 102 is about two times the distance between adjacent openings onthe visual line of openings formed between each pair of adjacent wallportions for FIG. 13.

Another alternative embodiment of the spacer of this invention is shownin FIG. 14. In this embodiment, a single spacer having a plurality ofhexagonal fuel rod receiving channels is formed to fit within ahexagonal fuel assembly shroud generally indicated by broken lines 111.Dimples 112 project into each channel I10. The spacer shown in FIG. 14adds a minimal amount of neutron absorbing material in the spacer. Thisspacer is formed as described above, with the preform trimmed to producethe generally hexagonal configuration. Many other variations on thebasic spacer of this invention will occur to those skilled in the art tomeet particular requirements and circumstances.

Although specific arrangements and proportions have been described inthe above description of typical embodiments, a wide variety ofarrangements and designs may be used as indicated above with similarresults.

Other modifications and ramifications of the present invention willoccur to those skilled in the art upon reading the present disclosure.These are intended to be included within the scope of this invention.

l claim:

1. A method of manufacturing a spacer for a nuclear reactor comprisingthe steps of:

a. forming a plurality of slits regularly spaced along parallel lines ona sheet material, each slit having a length of at least two times thedistance between pairs of slits, the center of each slit being locatedadjacent the space between slits of the next line of slits; and

b. simultaneously bending the sheet below each slit perpendicular tosaid slits displacing each portion of the sheet below each slit in thesame direction away from the original plane of said sheet whereby aplurality of channels having axes substantially parallel to each otherand to the plane of said sheet are formed.

2. The method according to claim 1 wherein each of said slits has alength of about three times the distance between pairs of adjacent slitsand said sheet is bent into a plurality of channels each having ahexagonal cross section.

3. The method according to claim 1 wherein each slit has a length ofabout twice the distance between pairs of adjacent slits and said sheetis bent into a plurality of channels each of which has a square crosssection.

4. The method of claim 1 further including the step of formingstrain-relief holes in said sheet at the ends of each slit.

5. The method of claim 1 further including the step of forming aplurality of dimples in said sheet, at least one of said dimplesprojecting into each channel.

: UNITED STATES PATENT UFFICE QETIFEQATE @F QRREQTEN Patent No.3,789,476 Dated February 5, 1974 Inventor(s) Ripley It is certified thaterror appears in the above-identified patent and that said LettersPatent are hereby corrected as shown below:

Column 1, line 63, "beteen" should be --between--., Column 2, A line.26, "improvd" should be --improved'--, Column 3, line 45, I after "of"insert -----a'---;' Column 4, line 2, after "14" insert -with each ofthe. numbers also representing one of a plurality of parellely spacedregularly deformed wall portions with each wall portion being displacedin a tiered manner from the adjacent wall portion,'-; and lines 4-8,delete "with each of the numbers also representing one of a plurality ofparallely spaced regularly deformed wall portions with each wall portionbeing displaced in a tiered manner from the adjacent .wall portion";line 4, insert a period after "Fig, 1""; and line 42, "beteween shouldbe --between'-, Column 6, line 18, "elvation" should be -elevation-; andline 57, delete "an" Column 7,- line 3, change "an" to' -a---a Column 8,line 24, change "95". to '--97- Signed and sealed thin 29th day ofOctober 1974.

(SEAL) Attes't:

McCOY M. GIBSON JR, C. MARSHALL DANN Attesting Officer Commissioner ofPatents FORM Do-1050 uo'sg) uscoMM-oc (wens-ps9 UNITED STATES PATENTOFFICE CERTIFICATE OF CORRECTION Patent: No. 3,789,476 Dated February 5.1974 Inventor(s) Ripley It is certified that error appears in theabove-identified patent and that said Letters Patent are herebycorrected as shown below:

Column 1, line 63, "beteen" should be -between--. Column 2, line .26,"improvd" should be --improved---. Column 3, line .45, I after "of"insert '--'a'--; Column 4, line 2, after "14'" insert -with each of thenumbers also representing one of a plurality of parellely spacedregularly deformed wall portions with each wall portion being displacedin a tiered manner from the adjacent .wall portion.'--; and lines '4-8,delete "with each of the numbers also representing one of a plurality ofparallelyspaced regularly deformed wall portions with each wall portionbeing displaced in a tiered manner from the adjacent wall portion"; line4, insert aperiod after "Fig. 1""; and line 42, "beteween" should be--between'--. Column 6, line 18, "elvation" should be elevation'--; andline 57, delete "an". Column 7, line 3, change "an" to' -*a--. Column 8,line 24, change "95" to '--97- Signed and sealed this 29th day ofOctober 1974.

(SEAL) Attest: I

McCOY M. GIBSON JR. c. MARSHALL DANN Attesting Officer Commissioner ofPatents FORM PO-IOSO (10-69) V USCOMMDC ans pug

1. A method of manufacturing a spacer for a nuclear reactor comprisingthe steps of: a. forming a plurality of slits regularly spaced alongparallel lines on a sheet material, each slit having a length of atleast two times the distance between pairs of slits, the center of eachslit being located adjacent the space between slits of the next line ofslits; and b. simultaneously bending the sheet below each slitperpendicular to said slits displacing each portion of the sheet beloweach slit in the same direction away from the original plane of saidsheet whereby a plurality of channels having axes substantially parallelto each other and to the plane of said sheet are formed.
 2. The methodaccording to claim 1 wherein each of said slits has a length of aboutthree times the distance between pairs of adjacent slits and said sheetis bent into a plurality of channels each having a hexagonal crosssection.
 3. The method according to claim 1 wherein each slit has alength of about twice the distance between pairs of adjacent slits andsaid sheet is bent into a plurality of channels each of which has asquare cross section.
 4. The method of claim 1 further including thestep of forming strain-relief holes in said sheet at the ends of eachslit.
 5. The method of claim 1 further including the step of forming aplurality of dimples in said sheet, at least one of said dimplesprojecting into each channel.